1. Field of the Invention
The present invention pertains to a method for hydraulic fracturing an earth formation from a deviated well by injecting a fluid having a relatively high viscosity at a relatively low injection rate to minimize the creation of multiple-fractures and near wellbore excess friction pressure losses.
2. Background
U.S. Pat. No. 5,074,359 issued Dec. 24, 1991 to Joseph H. Schmidt and assigned to the assignee of the present invention describes a hydraulic fracturing method for earth formations which are penetrated by inclined wellbores wherein the cased wellbore is perforated at the point of maximum tensile stress in the earth formation resulting from fracture initiation. The subject matter of U.S. Pat. No. 5,074,359 is incorporated herein by reference.
Although the '359 Patent describes a method for locating perforations in well casing at the best orientation for initiating a hydraulic fracture in the expected fracture propagation plane (i.e. a plane normal to the minimum in situ horizontal stress in the formation), a substantial amount of twisting or turning of the fracture or the initiation of multiple fractures may still exist in severely misoriented wellbores which, in turn, creates near-wellbore restrictions to the flow of fracturing fluids. A relatively unrestricted flow of fracturing fluid is usually necessary to create the fracture and carry a suitable amount proppant into the fracture so that suitable production of formation fluids through the fracture and into the well may eventually result. In many cases, a phenomenon known in the art as "screenout" results when the fracture proppant prematurely bridges the entrance region of the fracture due to twisting, turning or multiple fracture thereby causing the fluid injection pressure to rise rapidly and eventually exceed the pump or wellbore tubing pressure limits.
Conventional fracture designs focus on the creation of a fracture of desirable length, height and width. It is also desirable to increase fluid efficiency to reduce the amount of fluid to be used and to minimize damage to the proppant pack in the fracture. Such considerations typically lead to a fracture design using a reasonably high pump rate, if permissible, and as low a viscosity of the fracturing fluid as possible, bearing in mind viscosity requirement for the desired fracture size. However, relatively high, near wellbore friction pressure losses have been frequently observed in conventional fracture treatments of deviated wells. This friction pressure loss is indicative of a fracture with restriction in the near wellbore region which can be substantially detrimental to the success of the fracture treatment.
In fact, the relatively high pump rate fracture treatments in accordance with conventional design practices can result in the creation of multiple fractures in deviated wells. These multiple fractures are not desired because they result in near-wellbore restrictions which prevent the propagation of a fracture of substantial length and width so that a suitable proppant pack can be introduced into this fracture and the resultant flow of production fluids into the well will provide greater productivity. Contrary to conventional practice in the art of hydraulic fracturing of deviated wells, the present invention contemplates an improved method for hydraulically fracturing earth formations from deviated wells.